There is known a UWB (Ultra Wide Band) technique for a ultra wide band radio communication. In general, the UWB technique is used in a wireless TV, a wireless LAN system for a notebook PC (notebook personal computer) or portable information terminal (personal digital assistant), and the like. In general, communications using the UWB technique is expected to use a frequency band of 3.1 GHz to 4.9 GHz. To realize the communication using the UWB technique, an antenna compatible with UWB wireless communication is required.
As a conventionally known wide band antenna, there is a discone antenna 200′ as shown in FIG. 25. The discone antenna 200′ has a structure in which a disk 201′ and conical plate 202′ serving as a radiating element are fitted, in a manner as illustrated in FIG. 25, to a coaxial cable 203′ having a coaxial center conductor 204′ covered by a coaxial external conductor 205′.
Further, there is known, in addition to a 3D antenna as the discone antenna 200′, a planar antenna having a structure in which a radiating element is formed on a printed board. As an antenna technique of this type, the following Non-Patent Document 1 discloses a wide band antenna using a self-complementary radiating element. This antenna has a structure in which two patterns corresponding to two system-radiating elements of a dipole antenna are formed on a printed board. One of the two patterns is formed on the front surface of the printed board, and the other is formed on the back surface thereof in such a manner as not to face the pattern on the front surface.    Non-Patent Document 1: Journal of Institute of Electronics, Information and Communication Engineers (B) Vol. J88-B No. 9, September 2005, pages 1,662 to 1,673